In general, a large amount of heat enters and leaves a building through windows (openings). For example, about 48% of heat is lost through a window when a heater is used during winter, and up to about 71% of heat enters through a window when a cooler is used during summer. Accordingly, a large amount of energy can be saved by properly controlling light and heat that pass through a window.
Switchable sheets developed for such a purpose have a function to control inflow and outflow of light and heat.
Several types of light control elements are used for such switchable sheets. For example, there are light control elements using materials described below.
1) An electrochromic material whose optical transmittance reversibly changes when an electric current or a voltage is applied.
2) A thermochromic material whose optical transmittance changes depending on a temperature.
3) A gasochromic material whose optical transmittance is changed by controlling an atmospheric gas.
Research is most advanced on electrochromic switchable sheets using a light control element made of an electrochromic material such as a tungsten oxide thin film. The research is almost in a commercial stage, and there are products available on the market. However, to provide a sufficient optical characteristic to an electrochromic switchable sheet, a light control element having a multilayer thin film structure including, for example, five layers needs to be used. This in turn increases the costs of the electrochromic switchable sheet. On the other hand, the structure of a light control element for a gasochromic system is relatively simple compared with a light control element for an electrochromic switchable sheet. For this reason, a gasochromic system is expected to be a promising candidate that can be manufactured at low costs, and research is being conducted on materials of a light control element and a configuration of a gasochromic system (see, for example, Patent Documents 1-4).
In a related-art gasochromic system, a pair of glass sheets are bonded together via a spacer to form a path for supplying hydrogen to a light control element, and the light control element is provided on at least one of the facing surfaces of the glass sheets.